B&W images stored in pdf are too big

[Michel-nk]

When i save black and white image in PDF-format, xnview stores them in this manner:

...
/Type /XObject
/Subtype /Image
/Name /Im0
/Filter [ /ASCII85Decode ]
/Width XXXX
/Height YYYY
/ColorSpace 11 0 R
/BitsPerComponent 8
/Length 10 0 R
>>
stream
!<<*!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8
W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!
s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W
-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s
8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-!s8W-
...

and pdf's size becomes ... very very very monstrous.

But after converting source to grey, pdf becomes normal size.

Dear Author! Please, provide possibility to automatic(implicit) B&W to grey-scale image converting before putting it in PDF. Or fully change storage method for B&W images in PDF.

Thank you!

[xnview]

In greyscale, it's smaller because you use JPEG compression, right?

[Michel-nk]

In greyscale, it's smaller because you use JPEG compression, right?

Yes, right. But i can't apply this compression method to B&W-images when store them in PDF. How can i do this?

[xnview]

Yes, the only way is to convert them in greyscale before

[cday]

Black and white images saved as TIFFs with Fax compression can be very small -- much smaller than a grayscale JPEG -- and when a PDF file is created from a TIFF image, Fax is one of the compression option available.

I think you could be quite surprised at the small file sizes that result when a black and white image is saved as a TIFF, or a TIFF image saved as a PDF, when Fax compression is selected. Fax is also lossless compression, unlike JPEG, so even when the file size is very small there is no loss of quality.